The present invention relates to the field of gas furnaces, and in particular to monitoring pollutant levels in the vent system of a furnace and controlling operation of the furnace based on sensed pollutant levels.
Carbon monoxide (CO) may be produced during the combustion process in a malfunctioning gas heating appliance. If excessive CO is released into the heated space, it can cause health related issues for occupants of the heated space. In some conventional ambient air systems, a CO sensor is disposed within the heated space to sense CO levels, and could be configured to disable the flow of fuel to the furnace upon detection of unsafe levels of CO. However, this type of system will either disable the furnace indefinitely, or will cause it to cycle the furnace back on when CO levels are safe, then off again as CO levels rise. If a trip occurs during cold weather, and the building being heated remains unoccupied for a long period of time or a service person is not readily available, water fixtures and pipes can freeze up and burst, causing significant damage to the structure. In addition, if the furnace cycles on and off indefinitely, the cumulative buildup of CO could lead to extended periods of unsafe levels.